Loudspeakers are widely used for providing projection of voice and music in a variety of areas and for numerous purposes. One area in which loudspeakers are particularly important and have had substantial difficulty in providing good results is in large public areas. In such locations, the use of conventional loudspeakers is common, but there are difficulties because of the directional nature of the speakers"" sound projection. As a result, in order to assure maximum coverage, numerous or multiple speakers are employed with overlapping coverage areas which requires proper application engineering and often considerable expense to attain the desired results.
In an attempt to reduce the necessity of having numerous loudspeaker components installed to provide the desired coverage, loudspeakers having a hemispherical coverage pattern have been developed. Although many of these prior art loudspeakers had been able to provide a projection of voice and music over a wider listening area, numerous problems have continued to exist in producing products which achieve a true full frequency hemispherical sound projection pattern from a single overhead sound source, particularly in areas having a low ceiling.
One of the principal problems which has plagued prior art spherical coverage loudspeakers as well as conventional loudspeakers centers on the physical characteristics of acoustic wave patterns. In this regard, audio frequencies essentially occupy 11 octaves of the electromagnetic spectrum, with acoustical wave lengths varying across a ratio of more than 2000 to 1 (about 113 feet to about xc2xd in.). In most applications, a more reasonable and workable ratio is 1000 to 1 (about 56 feet to 0.68 inches). Regardless of which ratio is employed, it is apparent, due to their very nature, that these extremes of wave-length energy require the application and use of completely different areas and aspects of the laws of acoustical physics.
Another problem inherent in providing optimum projection of voice and music is the fact that lower frequencies of the audio spectrum produce spherical waves which tend to be fluid in nature and difficult to control in terms of shaping and directing. Furthermore, higher frequencies develop planar waves which exhibit directional characteristics and are, by their very nature, not easily dispersed or diffused into broad coverage patterns. Finally, midrange frequencies produce various combinations of these two extremes.
In attempting to overcome these prior art problems, while also providing maximum area coverage, spherical loudspeaker systems with shaped dishes or xe2x80x9creflectorsxe2x80x9d suffer from one or more shortcomings. One such common problem is a severe decrease of high frequency energy distribution at the wider points of coverage, typically beginning at about 45 degrees from the central axis. Another common problem is a significant increase in phase distortion from unwanted multiple reflections occurring between the sound source and the reflector, as well as a significant increase in intermodulation distortion due to the remodulation of one-wave by another of a different frequency. Furthermore, high intensity lobes of acoustic energy are often produced directly on axis with the reflector, expanding as wide as 20 to 30 degrees from the central axis.
Another problem typically countered with prior art overhead loudspeaker systems is the inability of such speaker systems to function as desired in low ceiling environments. Typically, in most applications, a low ceiling encompasses ceiling heights ranging between about 8 and 15 feet. In these applications, overhead loudspeaker system encounter substantially increased acoustical polar distribution problems due to the shorter linear distance between the sound source and the listener""s ears. Typically, in a low ceiling environment, the listener is placed within the acoustical xe2x80x9cnear fieldxe2x80x9d of the system where some, if not all, of the acoustical components of the loudspeaker are present at any one given point in space.
Typically, the xe2x80x9cfar fieldxe2x80x9d boundary is considered to begin, within the spatial field, at a point where the summation wave presents all of the attributes of the system""s design. The acoustical pattern shaping effects of the otherwise true hemispherical coverage loudspeaker system do not exist within the near field, but are present in their proper form and function in the far field. The summation wave defines that point in space where all of the acoustical wave shaping effects unify into one single wave front, typically referred to as the near field boundary, far field boundary, or summation boundary.
In many prior art systems, a concave progressive curved reflector is employed in order to obtain true hemispherical polar coverage. However, systems of this nature require higher ceilings to function properly, since a loudspeaker of this type must be placed at a listening distance which is at least eight times greater than the diameter of the reflector. Since most reflectors of this configuration are larger than 12 inches, the listening distance required for optimum performance would be greater than eight feet. As a result, the systems are highly effective in higher ceiling environments, but tend to be ineffective in low ceiling environments.
In general, prior art attempts to attain a true hemispherical spatial response in a low ceiling environment have resulted in compromised designs. Typically, these prior art systems incorporate one or more of the following shortcomings. One such common shortcoming is the existence of a high intensity lobe of acoustic energy directly on axis with the reflector. Usually the lobe of acoustic energy ranges between about 30xc2x0 and 60xc2x0 about the central axis of the system.
In addition, another difficulty typically encountered in prior art systems is a severe decrease of high frequency energy distribution at the wider points of the coverage pattern, usually beginning at about 45xc2x0 from the central axis and continuing to about 90xc2x0 therefrom. Furthermore, a significant increase in phase distortion is created from undesirable multiple reflections between the sound source and the reflector. In addition, a significant increase in intermodulation distortion is created due to the remodulation of one wave by another wave of a different frequency. This, additionally, generates an undesirable phase distortion.
Further drawbacks typically encountered with prior art systems is frequency selective distribution of the reproduced signal which creates a reduced bandwidth, xe2x80x9clow fidelityxe2x80x9d condition and a subsequent loss of aural articulation and intelligibility. Finally, spectral imbalance of the distribution pattern is also found, particularly unequal levels of low, mid-range, and high frequency signals at various angles within the 180xc2x0 coverage pattern.
By employing the present invention, all of the difficulties and drawbacks of prior art loudspeaker constructions are eliminated and a low profile overhead loudspeaker system is achieved which controls and shapes the ultimate acoustical wave form produced thereby, achieving a system which is particularly wellsuited for use in low ceiling environments. In the present invention, a loudspeaker system is achieved which incorporates a uniquely constructed wave shaping and controlling member which is formed as an integral component of the speaker assembly. In this way, broad band, acoustical wave shaping and control is realized.
In accordance with a present invention, the wave shaping/controlling member is cooperatively associated with the drivers of the loudspeaker in a way which effects the critical acoustical loading and atmospheric coupling thereof, while controlling and shaping the ultimate acoustical wave form so that a hemispherical polar coverage pattern results. In the preferred configuration, the polar coverage pattern produced by the present invention is provided across the loudspeaker system""s entire power bandwidth, beginning at an approximate distance of about three times the diameter of the acoustical source. As a result, an eight inch diameter loudspeaker is capable of providing the desired acoustical wave front at about two feet.
In accordance with the present invention, the desired acoustical system is achieved by attaching the wave shaping and controlling member of the present invention directly to the loudspeaker cabinet typically employed for a low ceiling, overhead sound system, with one or more drivers or speaker motors mounted in the cabinet. The uniquely constructed wave shaping and controlling member is specifically designed to receive and distribute the acoustical energy of the loudspeaker""s driver so as to provide an acoustical energy field of a true broadband hemispherical pattern. Furthermore, the present invention produces the desired acoustical energy field within the system""s power bandwidth, at a point of summation of approximately three times the acoustical source diameter.
In the preferred embodiment of the present invention, the wave shaping and controlling member is designed to be rigidly or securely affixed to the front of the loudspeaker enclosure, mechanically attached to the baffle of the loud speaker, or otherwise built into the construction of the enclosure during the fabrication or molding process as a homogeneous or integral component thereof. Regardless of the construction employed, the unique geometric contours of the wave shaping/controlling member are designed and positioned in the required critical acoustical fashion in order to achieve the desired broadband hemispherical polar coverage pattern.
As is more fully detailed below, the wave shaping and controlling member of the present invention comprises a combination of singular acoustical shaping and distribution devices which are individually designed to control specific and applicable sound bands of the audio spectrum. In this way, individual functions are performed, with each function representing a factor of the final acoustical summation product produced by the wave shaping/controlling member.
By employing the present invention, a loudspeaker system is achieved which controls and defines the wave shape and coverage patterns of the various frequency band widths, utilizing the natural characteristics of the wave itself, with no forced or artificial control. By using the following three elements, namely (1) a driver, (2) an enclosure, and (3) a uniquely constructed wave shaping and controlling member, a synergistic interaction is achieved which produces true hemispherical coverage patterns across the entire rated power bandwidth of the loud speaker.
The invention accordingly comprises an article of manufacture possessing the features, properties, and relation of elements which will be exemplified in the article hereinafter described, and the scope of the invention will be indicated in the claims.